1-Chloro-2,2,2-trifluoroethane, 1,1-dichloro-2,2,2-trifluoroethane and 1-chloro-1,2,2,2-tetrafluoroethane, known in the trade under the designations F133a, F123 and F124 respectively, are obtained industrially by catalytic fluorination of chlorinated olefins like trichloroethylene or perchloroethylene or of fluorinated intermediates like 1,1,2-trichloro-2,2-difluoroethane (F122), it being possible for this operation to be carried out either in the gas phase or in the liquid phase.
In the liquid phase the reaction is generally catalysed with antimony halides (see, for example, European Patents 462 514 and 547 930, relating to F133a). Numerous catalysts have been proposed for gas-phase fluorination, especially Zn, Ni, Mn, Mg, Fe, Co or Cr oxides or halides, either in bulk or preferably deposited on supports such as alumina or fluorinated alumina (Patents EP 583 703, U.S. Pat. No. 5,026,930 and WO92/16480 in the case of F133a, and Patents FR 1 315 351 or JP 2157235 in the case of F123).
Although the selectivities of these fluorinations are generally good, the products obtained are nevertheless accompanied by a number of impurities, especially of more or less fluorinated compounds (CF.sub.2 ClCH.sub.2 Cl, CFCl.sub.2 CH.sub.2 Cl, CF.sub.3 CH.sub.2 F, CF.sub.3 CHCl.sub.2, CF.sub.3 CH.sub.3), of C.sub.2 olefins such as CF.sub.2 =CHCl, CF.sub.2 =CFCl, CF.sub.2 =CCl.sub.2 and CFCl=CCl.sub.2, and of C.sub.4 olefins such as CF.sub.3 CH=CHCF.sub.3, CF.sub.3 CH=CFCF.sub.3, CF.sub.3 CH=CClCF.sub.3 and CF.sub.3 CF=CClCF.sub.3.
These impurities are obtained in larger quantities in the gas-phase process and, in particular, in the case where this fluorination is carried out in the presence of oxygen, to stabilize the catalyst activity (Patent EP 583 703). Thus, in the course of a fluorination of trichloroethylene (TCE) on a bulk chromium oxide, in the following conditions:
Temperature: 350.degree. C. PA1 Pressure: 15 bars PA1 Contact time: 14 seconds PA1 HF/TCE molar ratio: 10 PA1 O.sub.2 /TCE molar ratio: 0.06 PA1 CF.sub.2 =CHCl (-17.7.degree. C.).fwdarw.CF.sub.2 ClCHCl.sub.2 (72.degree. C.) PA1 CF.sub.3 CH=CClCF.sub.3 (35.degree. C.).fwdarw.CF.sub.3 CHClCCl.sub.2 CF.sub.3 (104.degree. C.) PA1 CF.sub.3 CH=CHCF.sub.3 (8.5.degree. C.).fwdarw.CF.sub.3 CHClCHClCF.sub.3 (78.degree. C.) PA1 CF.sub.3 CH=CFCF.sub.3 (8.degree. C.).fwdarw.CF.sub.3 CHClCFClCF.sub.3 (67.degree. C. calc)
an F133a containing approximately 3% of C.sub.4 olefinic products (essentially CF.sub.3 CH=CHCF.sub.3) was obtained.
These C.sub.4 impurities are particularly difficult to remove because they have volatilities which are very close to those of the products sought after, especially of F133a or F123, and some of them are particularly toxic.
F123 is employed in the refrigeration industry, in particular in air-conditioning plants. It is also employed as a synthesis intermediate.
F133a is employed industrially as an intermediate product for the manufacture of HALOTHANE CF.sub.3 CHBrCl, which is an anaesthetic agent, or for the manufacture of trifluoroethanol CF.sub.3 CH.sub.2 OH which itself is used essentially for the manufacture of other anaesthetic agents like ISOFLURANE (CF.sub.3 CHClOCHF.sub.2) and DESFLURANE (CF.sub.3 CHFOCHF.sub.2). The purity standards required for these products are such that it is advantageous to employ an F133a which is as pure as possible and which in particular contains no products capable of yielding toxic impurities.
Another essential application of F133a is at the present time the industrial manufacture of 1,1,1,2-tetrafluoroethane (F134a), one of the hydrofluoroalkanes which have replaced the chlorofluoroalkanes because of the impact of the latter on the stratospheric ozone layer.
The fluorination of F133a to F134a is generally carried out in the gas phase at temperatures of the order of 350-400.degree. C., in the presence of an excess of HF.
A number of olefinic impurities formed during this fluorination of F133a to F134a are the same ones as those liable to be formed during the manufacture of F133a and to preexist in the F133a employed as raw material for this second fluorination.
The purification of F123 and, in particular, the removal of its olefinic impurities have been carried out with the aid of oxidizing agents such as alkali metal permanganates (Patent EP 357 328) or by passing over metal oxides at temperatures which are preferably between 90 and 130.degree. C. (Patent EP 370 688) or else by treatment with the aid of hydrides and/or strong bases (Patent EP 493 760).
Like other hydrochlorofluorocarbons, F123 and F124 can also be rid of their olefinic impurities by catalytic hydrogenation as indicated in Patent Application WO 93/14052.
To our knowledge, no document exists describing a process for specific purification of F133a and, in particular, a removal of olefins present in F133a.